Force detection in touch devices using piezoelectric sensors

ABSTRACT

Systems and methods related to piezoelectric based force sensing in touch devices are presented. One embodiment, for example, may take the form of an apparatus including a touch device having a deformable device stack and a piezoelectric element positioned relative to the deformable device stack such that the piezoelectric element deforms with the deformable stack. Deformation of the piezoelectric element generates a signal having a magnitude discernable as representative of an amount of force applied to the touch device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 application of PCT/US2013/032607,filed Mar. 15, 2013, and entitled “Force Detection in Touch DevicesUsing Piezoelectric Sensors,” and further claims the benefit under 35U.S.C. § 119(e) to U.S. provisional application No. 61/738,381, filedDec. 17, 2012, and entitled “Force Detection In Touch Devices UsingPiezoelectric Sensors,” both of which are incorporated by reference asif fully disclosed herein.

Force Detection In Touch Devices Using Piezoelectric Sensors

BACKGROUND

The present application is directed to force detection and, morespecifically, to force detection using a piezoelectric sensor.

Background

Touch displays have become increasingly popular in electronic devices.Smart phones, cell phones, tablet computers, notebook computers, andcomputer monitors, and so forth, are increasingly equipped with displaysthat are configured to sense touch as a user input. The touch may besensed in accordance with one of several different touch sensingtechniques including, but not limited to, capacitive touch sensing.

Touch sensitive devices generally provide position identification ofwhere the user touches the device. The touching may include movement,gestures, and other effects related to position detection. For example,touch sensitive devices can provide information to a computing systemregarding user interaction with a graphical user interface (GUI) of adisplay, such as pointing to elements, reorienting or repositioningelements, editing or typing, and other GUI features. In another example,touch sensitive devices can provide information to a computing systemfor a user to interact with an application program, such as relating toinput or manipulation of animation, photographs, pictures, slidepresentations, sound, text, other audiovisual elements, and so forth.

While the touch sensitive devices provide an input mechanism thatprovides an appearance that the user is interacting directly withelement displayed in the GUI, the input is generally limited to the x-,y-positioning of the touch. In some cases, the input sensitivity hasbeen increased to allow for multi-touch inputs, but this is stilllimited to positional constraints of the surface upon which the touch issensed. Some applications and programs may benefit from additional inputmodes beyond that provided strictly by the touch sensing.

SUMMARY

The present application includes techniques directed to additional inputmodes for touch devices. In particular, embodiments may be directed tosensing force on a touch device using piezoelectric sensors. The forcesensing may be in addition to the touch sensing to enable an additionaluser input mode for the touch device.

One embodiment, for example, may take the form of an apparatus includinga touch device having a deformable device stack and a piezoelectricelement positioned relative to the deformable device stack such that thepiezoelectric element deforms with the deformable stack. Deformation ofthe piezoelectric element generates a signal having a magnitudediscernable as representative of an amount of force applied to the touchdevice.

Another embodiment may take the form of a touch device having adielectric cover glass (CG). The touch device further includes apiezoelectric structure adjacent the cover glass. The piezoelectricstructure includes piezoelectric material, a first set of electrodes ona first surface of the piezoelectric material, and a second set ofelectrodes on a second surface of the piezoelectric material and locatedbetween the piezoelectric material and the cover glass. Thepiezoelectric material is a dielectric material and the second set ofelectrodes is configured to sense both electrical charge generated bythe piezoelectric material and capacitance when a conductive material isbrought into proximity with the cover glass.

As an alternative to the above, a single piezoelectric structure may beused and placed on one side of the CG. A set of electrodes may besandwiched by the CG and the piezoelectric material. In such anembodiment, touch locations may be determined by a capacitive-sensingstructure associated with the CG, while force may be estimated based onthe lateral stretching of the electrodes operating in a d₃₃ mode.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following Detailed Description. As will be realized, the embodimentsare capable of modifications in various aspects, all without departingfrom the spirit and scope of the embodiments. Accordingly, the drawingsand detailed description are to be regarded as illustrative in natureand not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front perspective view of a first example of a computingdevice incorporating a force sensing device.

FIG. 1B is a front perspective view of a second example of a computingdevice incorporating a force sensing device.

FIG. 1C is a front elevation view of a third example of a computingdevice incorporating the force sensing device.

FIG. 2 is a simplified cross-section view of the computing device takenalong line 2-2 in FIG. 1A.

FIG. 3 is a block diagram of an example touch I/O device and a hostcomputing system.

FIG. 4 is a block diagram of an example system that includes a touch I/Osubsystem with force sensing.

FIG. 5A is a cross-sectional view of device of FIG. 1C taken along line5-5 and illustrating a display stack with piezoelectric element forforce sensing.

FIG. 5B illustrates the device stack of FIG. 5A deflecting due to forceand stretching the piezoelectric element.

FIG. 6A is a cross-sectional view of device of FIG. 1C taken along line5-5 and illustrating a display stack with piezoelectric element forforce sensing positioned directly under the cover glass in accordancewith an alternative embodiment.

FIG. 6B illustrates the device stack of FIG. 6A deflecting due to forceand stretching the piezoelectric element.

FIG. 7 illustrates a display stack and an electrode of a piezoelectricelement with terminals for connecting into a component and/or systemarchitecture.

FIG. 8 illustrates a display stack with a set of electrodes of apiezoelectric element in accordance with an alternative embodiment,wherein the set of electrodes take the form of strips of conductivematerial.

FIG. 9 illustrates a piezoelectric element with electrodes on opposingsides of the element to sense a generated electrical charge.

FIG. 10 illustrates an alternative embodiment in which top and bottomelectrodes on a piezoelectric element run in the same direction.

FIG. 11 illustrates an embodiment in which multiple, discretepiezoelectric elements are provided with discrete electrodes.

FIG. 12 illustrates an embodiment in which multiple piezoelectricelements are provide with an electrode sheet positioned therebetween.

FIG. 13 generally illustrates a schematic of the electrical componentsof the piezoelectric force and touch sensor.

FIG. 14A is a first example of a timing diagram for the computingdevice.

FIG. 14B is a second example of a timing diagram for the computingdevice.

FIG. 14C is a third example of a timing diagram for the computingdevice.

DETAILED DESCRIPTION

As alluded to above, when interfacing with a GUI, or with an applicationprogram, it may be advantageous for the user to be able to indicate anamount of force applied when manipulating, moving, pointing to,touching, or otherwise interacting with, a touch device. For example, itmight be advantageous for the user to be able to manipulate a screenelement or other object in a first way with a relatively lighter touch,or in a second way with a relatively more forceful or sharper touch. Inone such case, it might be advantageous if the user could move a screenelement or other object with a relatively lighter touch, while the usercould alternatively invoke or select that same screen element or otherobject with a relatively more forceful or sharper touch. Hence, havingthe ability to sense force might provide the touch device with greatercapabilities, with additional input information for the touch device.

In some embodiments, the force sensing device may be incorporated into avariety of electronic or computing devices, such as, but not limited to,computers, smart phones, tablet computers, track pads, and so on. Theforce sensing device may be used to detect one or more user force inputson an input surface and then a processor (or processing element) maycorrelate the sensed inputs into a force measurement and provide thoseinputs to the computing device. In some embodiments, the force sensingdevice may be used to determine force inputs to a track pad, a displayscreen, or other input surface.

The force sensing device may include an input surface, a force sensingmodule, a substrate or support layer, and optionally a sensing layerthat may detect another input characteristic than the force sensinglayer. The input surface provides an engagement surface for a user, suchas the external surface of a track pad or the cover glass for a display.In other words, the input surface may receive one or more user inputsdirectly or indirectly.

The force sensing module may include an ultrasonic module or sensor thatmay emit and detect ultrasonic pulses. In one example, the ultrasonicmodule may include a plurality of sensing elements arranged in rows orcolumns, where each of the sensing elements may selectively emit anultrasonic pulse or other signal. The pulse may be transmitted throughthe components of the force sensing device, such as through the sensinglayer and the input surface. When the pulse reaches the input surface,it may be reflected by a portion of the user (e.g., finger) or otherobject, which may reflect the pulse. The reflection of the pulse mayvary based on distance that the particular sensing element receiving thepulse is from the input. Additionally, the degree of attenuation of thepulse may also be associated with a force magnitude associated with theinput. For example, generally, as the input force on the input surfaceincreases, the contacting object exerting the force may absorb a largerpercentage of the pulse, such that the reflected pulse may be diminishedcorrespondingly.

In embodiments where it is present, the sensing layer may be configuredto sense characteristics different from the force sensing module. Forexample, the sensing layer may include capacitive sensors or othersensing elements. In a specific implantation, a multi-touch sensinglayer may be incorporated into the force sensing device and may be usedto enhance data regarding user inputs. As an example, touch inputsdetected by the sense layer may be used to further refine the forceinput location, confirm the force input location, and/or correlate theforce input to an input location. In the last example, the forcesensitive device may not use the capacitive sensing of the force sensingdevice to estimate a location, which may reduce the processing requiredfor the force sensing device. Additionally, in some embodiments, a touchsensitive device may be used to determine force inputs for a number ofdifferent touches. For example, the touch positions and force inputs maybe used to estimate the input force at each touch location.

In some specific embodiments described herein piezoelectric sensors maybe used to determine a force applied to the touch device. In particular,a d₃₁ sensing mode of piezoelectric sensors may be utilized as a measureof the force applied to the touch device. The d₃₁ sensing mode isrelated to the stretching of the piezoelectric, as will be discussed ingreater detail below with reference to example embodiments. In someembodiments, a d₃₃ sensing mode of piezoelectric sensors may be utilizedin addition to or in lieu of the d₃₁ mode. The d₃₃ sensing mode isrelated to the compression of the piezoelectric sensor and, as such, mayoperate as a secondary piezoelectric effect adding to the total chargegenerated as the piezoelectric sensor stretches during a force sensingevent.

The piezoelectric sensors may generally be configured to sensedeformation of a touch display stack. As such, the piezoelectric sensorsmay be located within the display stack or attached to stack (e.g.,laminated to the bottom of the display stack). For displays that includea backlight, such as a liquid crystal display (LCD), the piezoelectricsensor may be located between a rear polarizer and the backlight.Alternately, the piezoelectric sensor may be located on the back of thecover glass, whether or not the system includes a backlight.

FORCE SENSITIVE DEVICE AND SYSTEM

Turning now to the figures, illustrative electronic devices that mayincorporate the force sensing device will be discussed in more detail.FIGS. 1A-1C illustrate various computing or electronic devices that mayincorporate the force sensing device. With reference to FIG. 1A, theforce sensing device may be incorporated into a computer 10, such as alaptop or desktop computer. The computer 10 may include a track pad 12or other input surface, a display 14, and an enclosure 16 or frame. Theenclosure 16 may extend around a portion of the track pad 12 and/ordisplay 14. In the embodiment illustrated in FIG. 1A, the force sensingdevice may be incorporated into the track pad 12, the display 14, orboth the track pad 12 and the display 14. In these embodiments, theforce sensing device may be configured to detect force inputs to thetrack pad 12 and/or the display 14.

In some embodiments, the force sensing device may be incorporated into atablet computer. FIG. 1B is a top perspective view of a tablet computerincluding the force sensing device. With reference to FIG. 1B, the tablecomputer 10 may include the display 14 where the force sensing device isconfigured to detect force inputs to the display 14. In addition to theforce sensing device, the display 14 may also include one or more touchsensors, such as a multi-touch capacitive grid, or the like. In theseembodiments, the display 14 may detect both force inputs, as well asposition or touch inputs.

In yet other embodiments, the force sensing device may be incorporatedinto a mobile computing device, such as a smart phone. FIG. 1C is aperspective view of a smart phone including the force sensing device.With reference to FIG. 1C, the smart phone 10 may include a display 14and a frame or enclosure 16 substantially surrounding a perimeter of thedisplay 14. In the embodiment illustrated in FIG. 1C, the force sensingdevice may be incorporated into the display 14. Similarly to theembodiment illustrated in FIG. 1B, in instances where the force sensingdevice may be incorporated into the display 14, the display 14 may alsoinclude one or more position or touch sensing devices in addition to theforce sensing device.

Additionally, the device 10 may include one or more buttons 15 and/orother input devices. In some embodiments, the button 15 may take theform of a home button. Further, in some embodiments, the button 15 maybe integrated as part of a cover glass of the device and thepiezoelectric based force measurements may be utilized to determineactuation of the button.

The force sensing device will now be discussed in more detail. FIG. 2 isa simplified cross-section view of the electronic device taken alongline 2-2 in FIG. 1A. With reference to FIG. 2, the force sensing device18 may include an input surface 20, a sensing layer 22, a force sensingmodule 24 or layer, and a substrate 28. As discussed above with respectto FIGS. 1A-1C, the input surface 20 may form an exterior surface (or asurface in communication with an exterior surface) of the track pad 12,the display 14, or other portions (such as the enclosure) of thecomputing device 10. In some embodiments, the input surface 20 may be atleast partially translucent. For example, in embodiments where the forcesensing device 18 is incorporated into a portion of the display 14.

The sensing layer 22 may be configured to sense one or more parameterscorrelated to a user input. In some embodiments, the sensing layer 22may be configured to sense characteristics or parameters that may bedifferent from the characteristics sensed by the force sensing module24. For example, the sensing layer 22 may include one or more capacitivesensors that may be configured to detect input touches, e.g.,multi-touch input surface including intersecting rows and columns. Thesensing layer 22 may be omitted where additional data regarding the userinputs may not be desired. Additionally, the sensing layer 22 mayprovide additional data that may be used to enhance data sensed by theforce sensing module 24 or may be different from the force sensingmodule. In some embodiments, there may be an air gap between the sensinglayer 22 and the force sensing module 24. In other words, the forcesensing module 24 and sensing layer may be spatially separated from eachother defining a gap or spacing distance.

The substrate 28 may be substantially any support surface, such as aportion of an printed circuit board, the enclosure 16 or frame, or thelike. Additionally, the substrate 28 may be configured to surround or atleast partially surround one more sides of the sensing device 18.

In some embodiments, a display (e.g., a liquid crystal display) may bepositioned beneath the input surface 20 or may form a portion of theinput surface 20. Alternatively, the display may be positioned betweenother layers of the force sensing device. In these embodiments, visualoutput provided by the display may be visible through the input surface20.

As generally discussed above, the force sensing device may beincorporated into one or more touch sensitive device. It should beappreciated that although FIGS. 1A-1C illustrate specific examples ofelectronic devices, the techniques described herein may be applied tovarious other types of devices may implement the force measurementtechniques described herein. For example, a notebook computer, tabletcomputers, desktop computers, track pads and so forth, all may implementpiezoelectric based force measurement techniques, such as thosediscussed herein.

FIG. 3 illustrates an example block diagram showing an exampleembodiment including touch I/O device 1006 that can receive touch inputfor interacting with a computing system 1008. The touch I/O device 1006may be the computing device 10 illustrated in FIGS. 1A-1C, or may beincorporated into the computing device 10. The communication may be viaa wired or wireless communication channel 1010. Touch I/O device 1006may be used to provide user input to computing system 1008 in lieu of orin combination with other input devices such as a keyboard, mouse, etc.One or more touch I/O devices 1006 may be used for providing user inputto computing system 1008. Touch I/O device 1006 may be an integral partof computing system 1008 (e.g., touch screen on a laptop) or may beseparate from computing system 1008.

Touch I/O device 1006 may include a touch sensitive panel which iswholly or partially transparent, semitransparent, non-transparent,opaque or any combination thereof. Touch I/O device 1006 may be embodiedas a touch screen, touch pad, a touch screen functioning as a touch pad(e.g., a touch screen replacing the touchpad of a laptop), a touchscreen or touchpad combined or incorporated with any other input device(e.g., a touch screen or touchpad disposed on a keyboard) or anymulti-dimensional object having a touch sensitive surface for receivingtouch input.

In one example, touch I/O device 1006 embodied as a touch screen mayinclude a transparent and/or semitransparent touch sensitive panelpartially or wholly positioned over at least a portion of a display.According to this embodiment, touch I/O device 1006 functions to displaygraphical data transmitted from computing system 1008 (and/or anothersource) and also functions to receive user input. In other embodiments,touch I/O device 1006 may be embodied as an integrated touch screenwhere touch sensitive components/devices are integral with displaycomponents/devices. In still other embodiments a touch screen may beused as a supplemental or additional display screen for displayingsupplemental or the same graphical data as a primary display and toreceive touch input.

Touch I/O device 1006 may be configured to detect the location of one ormore touches or near touches on device 1006 based on capacitive,resistive, optical, acoustic, inductive, mechanical, chemicalmeasurements, or any phenomena that can be measured with respect to theoccurrences of the one or more touches or near touches in proximity todeice 1006. Software, hardware, firmware or any combination thereof maybe used to process the measurements of the detected touches to identifyand track one or more gestures. A gesture may correspond to stationaryor non-stationary, single or multiple, touches or near touches on touchI/O device 1006. A gesture may be performed by moving one or morefingers or other objects in a particular manner on touch I/O device 1006such as tapping, pressing, rocking, scrubbing, twisting, changingorientation, pressing with varying pressure and the like at essentiallythe same time, contiguously, or consecutively. A gesture may becharacterized by, but is not limited to a pinching, sliding, swiping,rotating, flexing, dragging, or tapping motion between or with any otherfinger or fingers. A single gesture may be performed with one or morehands, by one or more users, or any combination thereof.

Computing system 1008 may drive a display with graphical data to displaya graphical user interface (GUI). The GUI may be configured to receivetouch input via touch I/O device 1006. Embodied as a touch screen, touchI/O device 1006 may display the GUI. Alternatively, the GUI may bedisplayed on a display separate from touch I/O device 1006. The GUI mayinclude graphical elements displayed at particular locations within theinterface. Graphical elements may include but are not limited to avariety of displayed virtual input devices including virtual scrollwheels, a virtual keyboard, virtual knobs, virtual buttons, any virtualUI, and the like.

A user may perform gestures at one or more particular locations on touchI/O device 1006 which may be associated with the graphical elements ofthe GUI. In other embodiments, the user may perform gestures at one ormore locations that are independent of the locations of graphicalelements of the GUI. Gestures performed on touch I/O device 1006 maydirectly or indirectly manipulate, control, modify, move, actuate,initiate or generally affect graphical elements such as cursors, icons,media files, lists, text, all or portions of images, or the like withinthe GUI. For instance, in the case of a touch screen, a user maydirectly interact with a graphical element by performing a gesture overthe graphical element on the touch screen. Alternatively, a touch padgenerally provides indirect interaction.

Gestures may also affect non-displayed GUI elements (e.g., causing userinterfaces to appear) or may affect other actions within computingsystem 1008 (e.g., affect a state or mode of a GUI, application, oroperating system). Gestures may or may not be performed on touch I/Odevice 1006 in conjunction with a displayed cursor. For instance, in thecase in which gestures are performed on a touchpad, a cursor (orpointer) may be displayed on a display screen or touch screen and thecursor may be controlled via touch input on the touchpad to interactwith graphical objects on the display screen. In other embodiments inwhich gestures are performed directly on a touch screen, a user mayinteract directly with objects on the touch screen, with or without acursor or pointer being displayed on the touch screen.

Feedback may be provided to the user via communication channel 1010 inresponse to or based on the touch or near touches on touch I/O device1006. Feedback may be transmitted optically, mechanically, electrically,olfactory, acoustically, or the like or any combination thereof and in avariable or non-variable manner.

Attention is now directed towards embodiments of a system architecturethat may be embodied within any portable or non-portable deviceincluding but not limited to a communication device (e.g. mobile phone,smart phone), a multi-media device (e.g., MP3 player, TV, radio), aportable or handheld computer (e.g., tablet, netbook, laptop), a desktopcomputer, an All-In-One desktop, a peripheral device, or any othersystem or device adaptable to the inclusion of system architecture 2000,including combinations of two or more of these types of devices. FIG. 4is a block diagram of one embodiment of system 2000 that generallyincludes one or more computer-readable mediums 2001, processing system2004, Input/Output (I/O) subsystem 2006, radio frequency (RF) circuitry2008 and audio circuitry 2010. These components may be coupled by one ormore communication buses or signal lines 2003.

It should be apparent that the architecture shown in FIG. 4 is only oneexample architecture of system 2000, and that system 2000 could havemore or fewer components than shown, or a different configuration ofcomponents. The various components shown in FIG. 4 can be implemented inhardware, software, firmware or any combination thereof, including oneor more signal processing and/or application specific integratedcircuits.

RF circuitry 2008 is used to send and receive information over awireless link or network to one or more other devices and includeswell-known circuitry for performing this function. RF circuitry 2008 andaudio circuitry 2010 are coupled to processing system 2004 viaperipherals interface 2016. Interface 2016 includes various knowncomponents for establishing and maintaining communication betweenperipherals and processing system 2004. Audio circuitry 2010 is coupledto audio speaker 2050 and microphone 2052 and includes known circuitryfor processing voice signals received from interface 2016 to enable auser to communicate in real-time with other users. In some embodiments,audio circuitry 2010 includes a headphone jack (not shown).

Peripherals interface 2016 couples the input and output peripherals ofthe system to processor 2018 and computer-readable medium 2001. One ormore processors 2018 communicate with one or more computer-readablemediums 2001 via controller 2020. Computer-readable medium 2001 can beany device or medium that can store code and/or data for use by one ormore processors 2018. Medium 2001 can include a memory hierarchy,including but not limited to cache, main memory and secondary memory.The memory hierarchy can be implemented using any combination of RAM(e.g., SRAM, DRAM, DDRAM), ROM, FLASH, magnetic and/or optical storagedevices, such as disk drives, magnetic tape, CDs (compact disks) andDVDs (digital video discs). Medium 2001 may also include a transmissionmedium for carrying information-bearing signals indicative of computerinstructions or data (with or without a carrier wave upon which thesignals are modulated). For example, the transmission medium may includea communications network, including but not limited to the Internet(also referred to as the World Wide Web), intranet(s), Local AreaNetworks (LANs), Wide Local Area Networks (WLANs), Storage Area Networks(SANs), Metropolitan Area Networks (MAN) and the like.

One or more processors 2018 run various software components stored inmedium 2001 to perform various functions for system 2000. In someembodiments, the software components include operating system 2022,communication module (or set of instructions) 2024, touch processingmodule (or set of instructions) 2026, graphics module (or set ofinstructions) 2028, one or more applications (or set of instructions)2030, and force module (or set of instructions) 2038. Each of thesemodules and above noted applications correspond to a set of instructionsfor performing one or more functions described above and the methodsdescribed in this application (e.g., the computer-implemented methodsand other information processing methods described herein). Thesemodules (i.e., sets of instructions) need not be implemented as separatesoftware programs, procedures or modules, and thus various subsets ofthese modules may be combined or otherwise re-arranged in variousembodiments. In some embodiments, medium 2001 may store a subset of themodules and data structures identified above. Furthermore, medium 2001may store additional modules and data structures not described above.

Operating system 2022 includes various procedures, sets of instructions,software components and/or drivers for controlling and managing generalsystem tasks (e.g., memory management, storage device control, powermanagement, etc.) and facilitates communication between various hardwareand software components.

Communication module 2024 facilitates communication with other devicesover one or more external ports 2036 or via RF circuitry 2008 andincludes various software components for handling data received from RFcircuitry 2008 and/or external port 2036.

Graphics module 2028 includes various known software components forrendering, animating and displaying graphical objects on a displaysurface. In embodiments in which touch I/O device 2012 is a touchsensitive display (e.g., touch screen), graphics module 2028 includescomponents for rendering, displaying, and animating objects on the touchsensitive display.

One or more applications 2030 can include any applications installed onsystem 2000, including without limitation, a browser, address book,contact list, email, instant messaging, word processing, keyboardemulation, widgets, JAVA-enabled applications, encryption, digitalrights management, voice recognition, voice replication, locationdetermination capability (such as that provided by the globalpositioning system (GPS)), a music player, etc.

Touch processing module 2026 includes various software components forperforming various tasks associated with touch I/O device 2012 includingbut not limited to receiving and processing touch input received fromI/O device 2012 via touch I/O device controller 2032.

System 2000 may further include force module 2038 for performing themethod/functions as described herein in connection with FIGS. 5-13.Force module 2038 may at least function to determine if a forcethreshold has been exceeded. Module 2038 may also interact withapplications, software, hardware and/or other devices within the system2000. Module 2038 may be embodied as hardware, software, firmware, orany combination thereof. Although module 2038 is shown to reside withinmedium 2001, all or portions of module 2038 may be embodied within othercomponents within system 2000 or may be wholly embodied as a separatecomponent within system 2000.

The force module 2038 may generally relate to interpretation of forcemeasurements and/or their effect on the current operating context of thesystem 2000. Generally, the force module 2038 and the touch processingmodule 2026 may be configured to operate in cooperation to determine theeffect of a force measurement. For example, the touch processing module2026 may be utilized to help discern a location of touch on a surface.This location information may be used in determining an effect of aforce measurement. Specifically, if a threshold amount of force issensed over the button 15 (FIG. 10), it may actuate the button, whereasthe same force at a different location would not actuate the button.Moreover, the cooperation between the touch and force modules allowsmulti-force discernment in some embodiments. For example, similar tomulti-touch, a determination of a threshold amount of force in multiplelocations on the surface may be interpreted as a particular user inputdifferent from a threshold force measured at a single location. Itshould be appreciated that in some embodiments, the touch and forcemodules may operate entirely independently from each other.

I/O subsystem 2006 is coupled to touch I/O device 2012, thepiezoelectric sensor 2042 and one or more other I/O devices 2014 forcontrolling or performing various functions. Touch I/O device 2012communicates with processing system 2004 via touch I/O device controller2032, which includes various components for processing user touch input(e.g., scanning hardware). The piezoelectric sensor 2042 is communicateswith piezoelectric controllers 2043 as part of the force determinationfor force measurements. In particular, for example, signals generated bythe piezoelectric sensor 2042 are controlled or otherwise received bythe piezoelectric controller 2043 as part of the I/O subsystem 2006. Oneor more other input controllers 2034 receives/sends electrical signalsfrom/to other I/O devices 2014. Other I/O devices 2014 may includephysical buttons, dials, slider switches, sticks, keyboards, touch pads,additional display screens, or any combination thereof.

If embodied as a touch screen, touch I/O device 2012 displays visualoutput to the user in a GUI. The visual output may include text,graphics, video, and any combination thereof. Some or all of the visualoutput may correspond to user-interface objects. Touch I/O device 2012forms a touch-sensitive surface that accepts touch input from the user.Touch I/O device 2012 and touch screen controller 2032 (along with anyassociated modules and/or sets of instructions in medium 2001) detectsand tracks touches or near touches (and any movement or release of thetouch) on touch I/O device 2012 and converts the detected touch inputinto interaction with graphical objects, such as one or moreuser-interface objects. In the case in which device 2012 is embodied asa touch screen, the user can directly interact with graphical objectsthat are displayed on the touch screen. Alternatively, in the case inwhich device 2012 is embodied as a touch device other than a touchscreen (e.g., a touch pad) the user may indirectly interact withgraphical objects that are displayed on a separate display screenembodied as I/O device 2014.

Touch I/O device 2012 may be analogous to the multi-touch sensitivesurface described in the following U.S. Pat. Nos. 6,323,846; 6,570,557;and/or 6,677,932; and/or U.S. Patent Publication 2002/0015024A1, each ofwhich is hereby incorporated by reference.

Embodiments in which touch I/O device 2012 is a touch screen, the touchscreen may use LCD (liquid crystal display) technology, LPD (lightemitting polymer display) technology, OLED, or OEL (organic electroluminescence), although other display technologies may be used in otherembodiments.

Feedback may be provided by touch I/O device 2012 based on the user'stouch input as well as a state or states of what is being displayedand/or of the computing system. Feedback may be transmitted optically(e.g., light signal or displayed image), mechanically (e.g., hapticfeedback, touch feedback, force feedback, or the like), electrically(e.g., electrical stimulation), olfactory, acoustically (e.g., beep orthe like), or the like or any combination thereof and in a variable ornon-variable manner.

The I/O subsystem 2006 may include and/or be coupled to one or moresensors configured to be utilized in the force determination. Inparticular, the I/O subsystem 2006 may include an LED 3002 and a sensor3004, and/or an additional sensor 4000. Each of the LED 3002, sensor3004 and additional sensors 4000 may be coupled to the touch I/O devicecontroller 2032, or another I/O controller (not shown). The LED 3002,sensor 3004 and additional sensor 4000 may be utilized, for example, aspart of a proximity sense routine to determine if a user or object isclose the system. If the user or object is not near the system 2000, anyforce measurement and/or sensed touch may be false and, therefore,discarded.

System 2000 also includes power system 2044 for powering the varioushardware components and may include a power management system, one ormore power sources, a recharging system, a power failure detectioncircuit, a power converter or inverter, a power status indicator and anyother components typically associated with the generation, managementand distribution of power in portable devices.

In some embodiments, peripherals interface 2016, one or more processors2018, and memory controller 2020 may be implemented on a single chip,such as processing system 2004. In some other embodiments, they may beimplemented on separate chips.

Turning to FIG. 5A, a cross-sectional view taken along line 5-5 in FIG.10 illustrates layers of an example display stack 4010. Generally, thedisplay stack 4010 may include the display 14 of FIG. 10 and the layersthat constitute the display. For example, a top layer in the displaystack may be a cover glass 4012. The cover glass 4012 may be coupled toa front polarizer 4016, a display 4018, and a rear polarizer 4020 withsome adhesive 4014. The adhesive 4014 may be an optically clearadhesive. The front and rear polarizers 4016, 4020 may take any suitableform and may include polarizers that are known and used in the art. Apiezoelectric element 4022 or other force sensing element, may beattached to the rear polarizer in some embodiments. Attaching thepiezoelectric element 4022 to the rear polarizer 4020 allows thepiezoelectric element to deflect with the layers of the display stack4010 as it is subjected to force.

FIG. 5B illustrates a force (indicated by arrow 4024) applied to thedisplay stack 4010. The force causes the displacement or deflection ofthe layers of the display stack 4010. In particular, the cover glass4012 is deflected by the force and the deflection translates through theother layers in the stack. The deflection of the piezoelectric element4022 results in expansion or stretching of the piezoelectric element,thereby generating a signal. Specifically, in the case of apiezoelectric element, an electrical charge may be generated by thedeflection. Generally, the primary mode of charge generation may be ad₃₁ mode (e.g., the mode associated with the stretching of thepiezoelectric element 4022). The d₃₁ mode is illustrated by the arrow4026. A secondary mode of charge generation may be a d₃₃ mode whichgenerally is related to compression of the piezoelectric element 4022.It should be appreciated, however, that in some embodiments, the d₃₃mode may be a primary mode of charge generation and the d₃₁ mode may bea secondary mode.

In other embodiments, the piezoelectric elements may be located atdifferent positions within a display stack. The positioning may dependupon the type of display into which the piezoelectric element is placed.Additionally, or alternatively, the location of the piezoelectricelement within the stack may depend upon the optical characteristics ofthe piezoelectric element. For example, if the piezoelectric element mayhave a negative impact upon the image of the display, then it may bepreferable to position the piezoelectric behind the rear polarizer anddisplay.

FIG. 5A illustrates an embodiment in which a piezoelectric element 5022is positioned within a display stack 5010 directly under the cover glass5012. That is, the piezoelectric element 5022 is in front of theadhesive 5014, the front polarizer 5016, the display 5018 and the rearpolarizer 5020. FIG. 5B illustrates the deflection of the display stack5010 when a force 5024 is applied to the stack. The piezoelectricelement 5022 deflects with the cover glass 5012 causing stretching(arrow 5026) and generating a charge. In some cases, the piezoelectricmay deflect more sharply when mounted directly under the cover glassrelative to when it is mounted under the rear polarizer or other layerin the stack. However, the piezoelectric element 5022 should haveminimal optical effects. That is, the piezoelectric element 5022 istransparent and does not otherwise distort the image from the display5018.

The electrical structure that communicates the electrical charge fromthe piezoelectric elements may take any suitable form. Several differentembodiments, are presented herein as examples. FIG. 7 illustrates adisplay stack 6010 and an electrode 6012 of a piezoelectric element. Theillustrated electrode 6012 is a conductive sheet electrically coupledwith terminals 6014. In some embodiments, the terminals 6014 mayfunction as drive lines. It should be appreciated that the illustratedelectrode 6012 may take any suitable form may generally represent sheetelectrodes that may be located on either side of a piezoelectric elementto conduct the electrical charge generated by the piezoelectric elementto a controller or other device that may monitor changes to the chargegenerated by the piezoelectric.

FIG. 8 illustrates an alternative embodiment with a set of electrodes7012 that may take the form of strips of conductive material. The stripsof conductive material constituting the electrodes 7012 may be orientedin a generally parallel configuration. The use of the strips ofelectrodes may allow the force detection to be localized. That is, thelocation of the force input may be localized by the piezoelectricelement. The electrodes 7012 may be positioned at any suitable locationwithin the display stack 7010. The electrodes are also electricallycoupled to the terminals 7014. The terminals may function as drive linesin some embodiments.

FIG. 9 illustrates a piezoelectric element 8000 with electrodes onopposing sides of the element. A top set of electrodes 8010 may includeparallel electrodes and a bottom electrode may take the form of aconductive sheet 8012. In an alternative embodiment, the bottomelectrodes 8012 may take the form of a series of parallel electrodestrips extending in a direction perpendicular to that of the topelectrodes 8010.

FIG. 10 illustrates an alternative embodiment in which the topelectrodes 9010 and the bottom electrodes 9012 about a piezoelectricelement 9000 run in the same direction. That is, the electrodes 9010,9012 are conductive strips that are parallel with respect to otherelectrodes in the same layer and the electrodes on the opposite side ofthe piezoelectric element 9000.

FIG. 11 illustrates an embodiment in which multiple, discretepiezoelectric elements 10000 are provided. Each discrete piezoelectricelement 10000 has its own set of electrodes 10010, 10012. Thepiezoelectric elements 10000 and the electrodes 10010, 10012 may each beelongate members in some embodiments.

The piezoelectric elements 10000 may have a length so that they may becoupled to the display stack and flex when force is applied to thestack. In other embodiments, the piezoelectric elements 10000 and theelectrodes 10010, 10012 may take another geometrical form. For example,the piezoelectric elements 10000 may be cubical, rectangular or anyother shape. As such, the piezoelectric elements 10000 may be configuredas discrete pixels that may sense force at a particular location.

FIG. 12 illustrates an embodiment in which multiple piezoelectricelements are provide with an electrode sheet 10026 positionedtherebetween. A top piezoelectric element 10020 may have a set ofelectrodes 10024 having the form of electrically conductive stripsoriented in a first direction and a bottom piezoelectric element 10022has a set of electrodes 10028 having the form of electrically conductivestrips oriented in a second direction. The second direction may beoffset from the first direction by some offset angle. The seconddirection may generally be perpendicular to that of the first directionin some embodiments. This configuration may allow for location of aforce input to be discerned by the piezoelectric structure, as theelectrodes may generally form a grid and each electrode may be coupledto a discretely addressed input line. As one example, an active-matrixsensor arrangement may be employed, with field-effect transistors (orother suitable switches) at each row-column intersection. In such anembodiment, row/column conductors may interconnect the FETs and thepiezoelectric elements at the row and column intersections.Alternatively, a projective-scan type architecture may be employed.

In addition to the electrode strips discussed herein, an array or gridof smaller electrodes may be employed. Each electrode may function tosense force (or strain) separately from other electrodes in the arrayand may be driven and/or sensed separately from the other arrayelectrodes.

In each of the foregoing elements, the force measurement is derived frommeasuring local deformation. The local deformation is a function offorce translated through the cover glass and/or the display stack. Thatis, the display stack curves and the bottom of the stack strains (e.g.,stretches). Thus, the force measurement typically is not a measurementof the deflection or displacement of the stack or cover glass. Thepiezoelectric element of the sensors may be laminated to the bottom ofthe stack. In backlit displays, such as liquid crystal displays, thepiezoelectric elements may be located behind the rear polarizer, but infront of the backlight. Because they are located in front of thebacklight, they are generally transparent. The transistors andelectrodes associated with the piezoelectric elements may be formedthrough a process that provides for transparency, such as an indium tinoxide (ITO) deposition process. Additionally, as discussed above, apixel or grid geometry of electrodes may be created so that forcelocation may be determined. That is, a single film with many electrodesmay be used. In such embodiments, a multi-force determination may bemade, or an estimate of multi-force inputs may be approximated. That is,discrete, simultaneous force inputs at different locations may bediscerned.

Alternatively, the piezoelectric based sensors may be placed on the backof the display cover glass while providing the same advantages discussedabove.

It should be appreciated that embodiments discussed herein may beboundary-independent. That is, neither the piezoelectric film nor theelement to which it is applied (such as a display) need be bounded witha rubber or other elastic boundary, such as a gasket, in order tooperate. Instead, force determination may be performed even without sucha boundary.

As multiple modes of charge generation may be active (e.g., d₃₃ mode andd₃₁ mode), a calibration may be performed to account for both or allactive modes. Hence, the force determination may take into account allof the generated charge as a result of force, even if one mode isdominant. As one example of calibration, various known forces may beapplied to specific locations on the force-sensing surface of thedevice. This may occur, for example, in a factory prior to shipment orsale of the device. Force may be applied across the device's surface,including at locations near or on a boundary of the force-sensing area.The output of the piezoelectric sensors may be read out and generated asa strain map. This strain map may be used to calculate calibrationconstants for the different locations at which force was applied; sincethe applied forces are known, they may be correlated to the outputstrain map and the various constants required to scale the force to theoutput may be determined. Calibration constants may vary across theforce-sensing surface or may be relatively constant. Generally, thecalibration constants may relate sensor signal to force or strain toforce, and may be stored in a memory of the device. These constants maylater be retrieved and used to estimate a force applied to a particularlocation. Certain embodiments may employ plate deformation-basedalgorithms to correlate a deflection map of the force-sensing surface toone or more force inputs.

The piezoelectric elements generate their own signal and do not have tobe powered. However, the signal generated may generally be low energy.This low energy signal may be difficult to sense as there may be noiseand/or leakage in the circuit. The electrical model may take one ofseveral suitable forms. For example, in one embodiment, a high passfilter may be applied. However, the high pass filter effect may make lowfrequency elements in the signal difficult to read. In anotherembodiment, the signal may be amplified and/or processed to help obtainsuitable readings. For example, a low leakage op amp may be implementedto limit drift. Additionally, a shield may be provided in someembodiments to protect against capacitance from a user's finger. Forexample, a thin-film transistor layer in the display stack may begrounded to serve as a shield. Further, temperature changes may affectthe piezoelectric element and steps may be taken to mitigate anytemperature change impact. For example, temperature may be canceled outby using multiple sensors (e.g., one for thermal effect and the otherfor both thermal effects and force). For example, a dual mode rejectionmethod may be implemented. Alternatively, films that are not thermallysensitive may be used or a film that has a non-uniform directionalresponse may be used. The directional properties may be used to cancelout thermal effects. In one example, the films may be stacked orpositioned side by side so that their respective thermal effects canceleach other out.

As may be appreciated, in the presently disclosed embodiments thepiezoelectric element and electrodes are located within the displaystack and are not exposed. Additionally, the force sensing may notmerely be binary. Rather, force pixels may be sensed so that amulti-force parameter may be read.

In some embodiments, a force sensing structure may further be utilizedas a touch input structure. As piezoelectric elements are generallydielectric in nature (e.g., they are not conductive), they may beutilized as a dielectric member for a capacitor. That is, when a user'sfinger (or other capacitively-sensed element, such as a capacitivestylus) is in proximity to the cover glass surface, the position of thefinger/element may be sensed by the touch sensor. The touch sensor mayuse the piezoelectric element as one plane or part of amutual-capacitance array to detect such touches or near-touch events.Likewise, force applied to the cover glass may be translated into strainon the piezoelectric element, thereby generating a charge that may beread and utilized to approximate, estimate or otherwise measure theforce. This generated charge may further modulate the capacitance of thetouch sensor, and may be accounted for when detecting a touch event.Additionally, the cover glass of a device may serve as a dielectric foranother capacitive circuit. By multiplexing the operation of apiezoelectric element, it may function as both a force sensor and atouch sensor. In particular, the force and touch sensing structure maygenerally take the form of a piezoelectric structure with electrode(s)located on either side of the piezoelectric element. The sheets may beused to sense charge generated by deflection of the piezoelectricelements. Additionally, a top electrode(s) may be configured tocapacitively couple with a conductive element interacting with a displayscreen. For example, the electrode(s) may be configured to capacitivelycouple with a user's finger. The electrodes may be configured asself-capacitive members or mutual capacitive members (e.g., a bottomlayer may be non-patterned).

FIG. 13 generally illustrates a schematic of the electrical componentsof the piezoelectric force and touch sensor 10030. Generally, threeunique capacitive circuits may be created. A first capacitive circuit10032 may be parasitic in nature. That is, it may be incurred throughthe proximity of the electrodes of the piezoelectric element to anotherconductive layer or element. A second capacitive circuit 10034 may beformed by the parallel electrodes on either side of the piezoelectricelement. This capacitive circuit 10034 may be in parallel with theparasitic circuit 10032. A final capacitive circuit 10036 may be createdby bringing a capacitive element into proximity with a top electrode ofthe piezoelectric element. This capacitive circuit 10036 is in serieswith the other two capacitive circuits 10032, 10034. Changes in thiscapacitive circuit 10036 may be monitored to determine when a finger (orother capacitive element) is brought into proximity with the sensor10030 or touching a screen with which the sensor is associated. Thesensing operations may be multiplexed so that any time one of force ortouch is being sensed by the touch force sensor. The generated charge atthe piezoelectric element (e.g., the generated charge used to estimateforce) is not created due to a gap change. Rather, this charge may beproportional to the amount of force that is applied.

The piezoelectric based force sensor is an impulse sensor due to thenature of the piezoelectric element. That is, when the piezoelectricelement is deformed to generate a charge, the charge generated is animpulse signal. A circuit may be provided to integrate the impulsesignal and determine how much force is applied and how the forcechanges. Generally, the size of the generated impulse signal is linearlyrelated to the amount of force applied. The touch sensor, alternatively,does not generate an impulse signal.

The piezoelectric force and touch sensor 10030 may generally be createdby any suitable process. In one embodiment, ITO electrodes may be formedon an underside of a device cover glass. A piezoelectric element may bepositioned over the ITO electrodes and a second set of ITO electrodesmay be positioned or deposited on the piezoelectric element. The ITOelectrodes may take any suitable form. In one embodiment, the ITOelectrodes may be sheets. In another embodiment, the ITO may be stripsor pixels to enable a location determination of both the force and touchsensing. In some embodiments, the piezoelectric element and electrodesmay take the form of a piezoelectric package that may be installedbeneath a cover glass. Example piezoelectric films that may be utilizedin certain embodiments discussed herein include poly-L-lactic acidpiezoelectric (PLLA) elements, some of which are manufactured anddistributed by Murata Manufacturing Co., Ltd. One example of such a filmis a d₁₄ mode piezoelectric material cut in a 45 degree orientation inorder to permit operation in a d₃₁ mode. As another example, apolyvinylidene fluoride (PVDF) material may be used in certainapplications. In embodiments employing a PVDF material as a strainsensor, thermal effects on the PVDF may be accounted for, or the PVDFmay be thermally isolated.

The piezoelectric film may generally have a high transparency. Hence,the piezoelectric film generally does not appreciably impact the opticsof the system in which it is incorporated (at least as seen by the humaneye), which means it may be installed directly under the cover glass.This may prove advantageous, as it may be attached only to the coverglass rather than to other components or layers in a display stack.Therefore, the deformation of the piezoelectric element is dependentonly upon the deformation of the cover glass. Also, the film, or othertransparent piezoelectric element that may be installed directly underthe cover glass may be used with any display technology. That is, it isnot display device dependent. Additionally, because the force and touchsensor may be installed directly under the cover glass, there is nochange to existing display architecture. The piezoelectric based sensormay be directly inserted into existing architecture.

Timing Diagram

In some embodiments various components of the computing device and/ortouch screen device may be driven or activated separately from eachother and/or on separate frequencies. Separate drive times and/orfrequencies for certain components, such as the display, touch sensor orsensors (if any), and/or force sensors may help to reduce cross-talk andnoise in various components. FIGS. 14A-14C illustrate different timingdiagram examples, each will be discussed in turn below. It should benoted that the timing diagrams discussed herein are meant asillustrative only and many other timing diagrams and driving schemes areenvisioned.

With respect to FIG. 14A, in some embodiments, the display 14 and theforce sensor 18 may be driven substantially simultaneously, with thetouch sensitive component 1001 being driven separately. In other words,the driver circuits for the force sensing device 18 may be activatedduring a time period that the display is also activated. For example,the display signal 30 and the force sensing signal 34 may both be onduring a first time period and then may both inactive as the touchsensing device signal 32 is activated.

With respect to FIG. 14B, in some embodiments, the touch and forcedevices may be driven at substantially the same time and the display maybe driven separately. For example, the display signal 40 may be set high(e.g., active) during a time that the touch signal 42 and the forcesignal 44 may both be low (e.g., inactive), and the display signal 40may be low while both the touch signal 42 and the force signal 44 arehigh. In this example, the touch signal 42 and the force signal 44 mayhave different frequencies. In particular, the touch signal 42 may havea first frequency F1 and the force signal 44 may have a second frequencyF2. By utilizing separate frequencies F1 and F2, the computing devicemay be able to sample both touch inputs and force inputs atsubstantially the same time without one interfering with the other,which in turn may allow the processor to better correlate the touchinputs and the force inputs. In other words, the processor may be ableto correlate a force input to a touch input because the sensors may besampling at substantially the same time as one another. Additionally,the separate frequencies may reduce noise and cross-talk between the twosensors. Although the example in FIG. 14B is discussed with respect tothe force and touch signals, in other embodiments each of the drivesignal, the touch signal, and/or the force signal may have separatefrequencies from each other and may be activated simultaneously orcorrespondingly with another signal.

With respect to FIG. 14C, in some embodiments, various components in thecomputing device may be driven separately from one another. For example,the display signal 50 may be driven high, while both the touch signal 52and the force signal 54 are low. Additionally, the touch signal 52 maybe high while both the force signal 54 and the display signal 50 are lowand similarly the force signal 54 may be high while both the displaysignal 50 and the touch signal 52 are low. In these examples, the forcesignal's active period may be positioned between the active periods ofthe display and the touch sensor. In other words, the force sensor 18may be driven between the display being driven and the touch sensorsbeing driven. In these examples, each of the devices may be active atseparate times from one another, thereby reducing inter-system noise. Insome embodiments, the force sensor may have a shorter drive time thanthe display or touch signals; however, in other embodiments, the forcesensor may have a drive time that is substantially the same as or longerthan the display and/or touch sensor.

The foregoing describes some example techniques using piezoelectricelements to sense force in a touch sensitive stack. The sensing of forcegives an additional input mode for touch sensitive input devices.Although the foregoing discussion has presented specific embodiments,persons skilled in the art will recognize that changes may be made inform and detail without departing from the spirit and scope of theembodiments.

The invention claimed is:
 1. An apparatus comprising: an input surfaceconfigured to deform in response to a force exerted on the inputsurface; a display positioned below the input surface; a touch sensordisposed below and coupled to the input surface; and a piezoelectricelement array disposed below the display such that the piezoelectricelement array deforms with the input surface in response to the forceexerted, wherein the piezoelectric element array generates a signal inresponse to the deformation, the signal corresponding to a magnitude ofthe force exerted and configured to be multiplexed with an inactivestate of both the touch sensor and the display.
 2. The apparatus ofclaim 1, wherein the piezoelectric element array is configured tooperate with the touch sensor to determine a location of the exertedforce.
 3. The apparatus of claim 1, wherein the piezoelectric elementarray comprises a group of distributed electrodes.
 4. The apparatus ofclaim 1, wherein: the display comprises a backlight and a polarizer; andthe piezoelectric element array is positioned between the backlight andthe polarizer.
 5. The apparatus of claim 1, wherein the piezoelectricelement array is positioned on a back of the display.
 6. The apparatusof claim 1, wherein at least one element of the piezoelectric elementarray generates a signal as it is stretched due to deformation of theinput surface.
 7. The apparatus of claim 1, wherein at least one elementof the piezoelectric element array generates a signal as it iscompressed due to deformation of the input surface.
 8. The apparatus ofclaim 1, wherein the piezoelectric element array comprises a firstelectrode located on a first surface of a substrate and at a secondelectrode on a second surface of the substrate and aligned with thefirst electrode, wherein the second surface is opposite the firstsurface.
 9. The apparatus of claim 1, wherein the piezoelectric elementarray comprises a group of electrodes located on a first surface of asubstrate and at least one electrode on a second surface of thesubstrate, wherein the second surface is opposite the first surface. 10.The apparatus of claim 1, wherein the piezoelectric element arraycomprises a group of discrete piezoelectric structures, wherein eachpiezoelectric structure is associated with a corresponding set ofelectrodes.
 11. The apparatus of claim 1, wherein the piezoelectricelement array comprises a group of metal-oxide electrodes.
 12. Theapparatus of claim 11, wherein the group of metal-oxide electrodes isformed directly on the input surface.
 13. The apparatus of claim 1,wherein the piezoelectric element array comprises: a first piezoelectricstructure comprising a first set of elongated electrodes extendinglongitudinally in a first direction; a second piezoelectric structurecomprising a second set of elongated electrodes extending longitudinallyin a second direction; and an electrode located between the first andsecond piezoelectric structures.
 14. A touch device comprising: an outerprotective layer comprising a dielectric material; a display positionedbelow the outer protective layer; a piezoelectric structure below thedisplay, wherein the piezoelectric structure comprises: piezoelectricmaterial, wherein the piezoelectric material is a dielectric material; afirst set of electrodes, comprising at least two electrodes, on a firstsurface of the piezoelectric material; and a second set of electrodes,comprising at least two electrodes, on a second surface of thepiezoelectric material and located between the piezoelectric materialand the outer protective layer, the second set of electrodes configuredto sense both an electrical charge generated by the piezoelectricmaterial and a capacitance when a conductive material is brought intoproximity with the outer protective layer.
 15. The touch device of claim14, wherein the device is configured to multiplex a capacitive sensingoperation with a charge sensing operation.
 16. The touch device of claim14, wherein the piezoelectric material, first set of electrodes, andsecond set of electrodes comprise a film.
 17. The touch device of claim14, wherein the first and second set of electrodes are deposited on thepiezoelectric material.
 18. The touch device of claim 14, wherein thesecond set of electrodes are deposited on the outer protective layer.19. The touch device of claim 14, wherein the second set of electrodescomprise a set of discretely addressed electrodes so that a location ofboth a force measurement and a capacitive measurement is discernable.20. An apparatus comprising: an input surface to receive an exerteddownward force; a touch sensor disposed below the input surface; adisplay disposed below the touch sensor; a piezoelectric element arraydisposed below and extending across the display, the piezoelectricelement array configured to generate a signal corresponding to theexerted downward force and configured to be multiplexed with an inactivestate of both the touch sensor and the display.
 21. The apparatus ofclaim 20, wherein the piezoelectric element array is configured todetermine a magnitude of the exerted downward force.
 22. The apparatusof claim 20, wherein the piezoelectric element array is coupled to abacklight of the display.
 23. The apparatus of claim 20, wherein thepiezoelectric element array is positioned above a backlight of thedisplay, and positioned below a polarizer of the display.